This invention relates to semiconductor devices and more particularly to a method of manufacturing monocrystalline layers of silicon in such devices.
Monocrystalline silicon layers on substrates are used in many semiconductor devices. Such layers are useful for producing large area device arrays for flat panel displays, dielectrically insulated devices for high voltage and high frequency integrated devices and for many other applications. Such monocrystalline silicon layers have been produced by a method which involves first forming a sublayer of silicon dioxide on a substrate or a layer of another material which thermally matches the substrate, forming a recrystallizable layer of silicon on the sublayer, depositing at least one capping insulating layer on the recrystallizable silicon layer and then converting the recrystallizable silicon layer to a monocrystalline silicon layer. Typically such a conversion, involving melting and recrystallization may be carried out by radiation of a high intensity light or heat source such as a laser beam as described in J. G. K. Celler, J. Crystal Growth 53 (1980) 429-444 or by use of a strip heater as disclosed in M. W. Geis et al, Appl. Phys. Lett. 40 (2), January 1982, 158-160.
By use of methods well known in the semiconductor field, the monocrystalline silicon layer can then be fabricated for use in semiconductor devices.
The silicon dioxide sublayer provides a clean insulatng layer on top of the substrate and tends to reduce the tendency to cracking of the crystalline silicon layer due to the differences in thermal expansion coefficients between the substrate and the silicon layer. The capping layer acts to prevent agglomeration of the molten silicon during recrystallization and to prevent contamination of the polycrystalline silicon layer from atmospheric contaminants particularly during conversion of the recrystallizable layer to the monocrystalline layer and also acts as an insulator for the monocrystalline silicon layer during further fabrication.
However, the problem still exists of contamination of the recrystallized silicon layer by oxygen and other impurities from the capping layers and the sublayers particularly during conversion of the recrystallizable layer into the monocrystalline silicon layer. Further, the additional problem exists of the breaking up or the physical separation of the capping layer from the silicon layer during recrystallization.